Just buy an LED and a photocell, it really doesn't make that much of a difference! They will respond mostly the same. Note that more effecient LEDs will need less current for the same LDR response, but thats only a matter of adjusting the current limiting resistor.

Given our discussion the other day, I assume this is for an Anderton project.

It is possible to use other optoisolators and adjust other component values so that the whoe circuit behaves in a comparable way. For example, if you were trying to make an EPFM compressor, the LDR half of the optoisolator is used to set the gain of an op-amp stage by providing a second resistance in parallel with a 220k feedback resistor. If the LDR rsistance you end up using is noticeably less than the CLM6000 resistance, then you can simply reduce the 220k down to a lower value, like 150k or 100k, and change the value of the input resistor from 100k down to 47k. It's not the specific resistance of the CLM6000 that matters, but rather the impact of the combined parallel resistance, and its control over the gain, that matters.

In other cases, it can be that the recovery/settling time of the LDR in the CLM6000 is key to the sound, and here you might have to be picky.

In other cases, such as the EPFM phase shifter project, there might actually be more appropriate optoisolators, such as the Silonex NSL-32 units. The CLM6000s were selected originally because they have a certain lag built into them, whereby they take a little while to return to max resistance. That can be great for anything that uses them as part of a sidechain (compressor, noisegate, enfevelope filter), but is a little problematic for things like phasers or anything else that might use an LFO.